I was just thinking -- Titan has a very dense atmosphere and lower gravity than Earth, so it seems like parachutes could be very useful, and the Martian airbag/skycrane tricks wouldn't be necessary. Why aren't there plans for a Titan version of MER?

Landing on Titan is indeed comparatively easy. However - if you put an MER on Titan it would die, very very quickly. You've got a significant atmosphere which is far colder than Mars to deal with, thus need a much better insulated vehicle and a LOT of power for heaters etc. You also need a different power source, an RTG almost certainly. You could use some elements of the MER - but not the design per se. At that point, you're building something that looks more like MSL than MER. But a Titan rover wouldn't end up looking like MSL either I'd expect.

There isn't the money to do it. I'd love to see rovers everywhere. However - we've done one preliminary survey of Titan - we need a better survey, full panoramic imagery of a possible rover landing site, before we can contemplate sending a Rover up there.

The long answer is that ballooning is arguably a better, faster, cheaper way of getting around Titan.

There is no definitive cloud deck on Titan, the haze is omnipresent. While having to look through hundreds of km of it does impede visual instruments severely, it's not actually a thick fog as Huygens demonstrated. You can still see comfortably through several kilometers of it with slowly reducing contrast. A low altitude baloon would have no problem picking up the ground nor would a rover have difficulty seeing quite far out.

Another thing too. Mars takes just over 24 hours (or one earth day) to rotate and we can use the already present Mars orbiters to keep in constant contact with the rovers. But Titan takes 16 earth days for a full rotation. This means for 8 days of a Titan rotation, the rover is out of sight from Earth. So for full 16 day coverage, we would need a something orbiting Titan to make sure we get full coverage.

And another thing too. The one way light time to Titan is about 84 minutes, compared to Mars with 14 minutes.

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I call heaven and earth to witness against you this day, that I have set before thee life and death, the blessing and the curse; therefore choose life, that thou mayest live, thou and thy seed.

Interestingly, a rover could be made of metals relatively weak on Earth: tin and lead which gained enought structural stability under the cold conditions, when steel and aluminium get glasslike brittle. Supraconductivity would also be a surplus when designing electronics for titan. Insulating parts not to be very cold is not such a problem: double-walled compartments are commonly used in deep temperature technics ("Dewar bottles") for storing fluid gases like nitrogen and work also in an opposite direction: an dewar-like vehicle could be retain over-zero-temperatures for weeks. An excellent thermal insulation would cause another problem: to get rid of thermic energy produced by the systems.

Running RTGs on Titan will not create a havoc if distance to fluids is kept. Maybe heat radiating fins should be large and placed well above the ground.

With an well designed camera it would be possible to make color photos (a SSI-like camera would need 0.5 sec to take a well illuminated picture). The strange constructed Huygens-camera should not be considered as a non-plus-ultra.

The fluids on Titan are hydrocarbons; so there is not problem with short circuits when getting wet. With a correction lens (for refractive index) a camera arm could even look under "water". Nozzles spraying gasous helium or hydrogen could be used for cleaning and drying the optics.

Earthly biochemical compounds like amino acids, sugars and fats are completly inactiv at Titanian temperatures, and mostly unsoluble in liquid methane and ethane. There are only a few classes of active molecules at this deep temperature. A primary goal would be to get and concentrate them for analyzing purposes, maybe with a high performance liquid chromatograph and a mass spectrometer.

Supraconductivity would also be a surplus when designing electronics for titan.

How so?

QUOTE (Harkeppler @ Sep 13 2008, 05:14 PM)

With an well designed camera it would be possible to make color photos (a SSI-like camera would need 0.5 sec to take a well illuminated picture). The strange constructed Huygens-camera should not be considered as a non-plus-ultra.

I wasn't "strange", it's what they were able to do with the mass budget they had and the available bandwidth. Over and over again people don't realize how difficult it was to actually land something on Titan that needed to piggyback on one of the heaviest planetary spacecraft ever launched. Not to mention when the Huygens probe design actually started.

In any case, sending color imagers to Titan is less useful because the haze filters out a good portion of the solar spectrum, making everything look orange-yellow and constraining useful compositional analysis from local illumination. Unless you bring your own light source as Huygens did.

Non of the Huygens panorama images used the artificial light source which was aimed down and turned on near the surface. I don't think any of the images taken with that light were in focus, so they are not part of the usual Huygens image gallery seen. I don't know if they provided any useful spectroscopic data. (That's all just my recollection.)

Non of the Huygens panorama images used the artificial light source which was aimed down

I never said as much. I meant you need a light source if you wanted to do spectroscopy, which was the primary purpose of Huygens' lamp. My point is bringing a classic color imager (with filters wheels and all) is somewhat useless. As much as I like color images, having a panchromatic panoramic camera might be just as sufficient for a followup mission.

I wasn't "strange", it's what they were able to do with the mass budget they had and the available bandwidth. Over and over again people don't realize how difficult it was to actually land something on Titan that needed to piggyback on one of the heaviest planetary spacecraft ever launched. Not to mention when the Huygens probe design actually started.

It was more than strange: bad optic, misaligned rotation vains at the vessel, funny resolution, grotesque data compression producing weird artifacts... Optical investigation should be the prime objective instead of riddling years around what not was seen. A crucial problem seems to be in most planetary missions that the deliberatly long plannning, organizing and redefining phases are run over by the technical progress.

I do not see any useful effect of a crummy imager at all. And the Huygens imager is one, that can be proven with the test images gotten during parachuting experiments and even with the photos showing the parking lot under that university building - it is difficult to recognize even the lampposts there.

Besides this, the Huygens camera has nothing to do with the Cassini main craft at all, nothing with flight operations and nothing with landing procedures. It is a "development" made by several people influenced by these experts of a special German Max Planck Institute which is "famous" for constructing funny but not really functional exotics like the Giotto-Camera. By the way: Their last "progress" could be seen in form of the Rosetta NAC, which shut down during the Steins-encounter. Fascinating, like the Phoenix RAC which is unable to make color photos over a range of three feet due to the limited range of LEDs...

Instead of constructing bunches of not properly intergrated instruments with deginerīs flaws it would be necessary to come to a more comprehensive standard.

Interestingly, years before Cassini launches, someone has decided that the camera would not make it to the ground, so surface imaging was not a topic at all. Without any reason it was determined, that Titan has to be covered by oceans or mud. The Huygens camera sent around 130 identical frames from the surface which are not giving increasing detail after adding due to the coarse compression artifacts. With a small turnable mirror and double resolution, four to ten more useful photos would have been possible showing a partially Titan panorama - with the same Cassini mass and the same bandwith.

"If there would be elephants on Titan, the Huygens imager would not have seen them", as it was stated by a french newspaper, which writer seems not to be payed for that destinct remark.

Furthermore, color imagery is an interesting perspective at all, especially in that strange chemical environment. Which the argument "atmospherical absorption" any color planetary camera could be thrown away, but I am glad that the soviet scientist had put some simple constructed ones onto the Venera lander 13 and 14 at all.

Designing missions in retrospective, using other people's money, and risking other people's careers is easy, but not very constructive.In 3008, when Titan will be a popular tourist destination, our descendants will take all the photos they want.

I'm not 100% sure about it being a popular tourist destination...with the hydrocarbons in the atmosphere and the cold temperatures, I think Earthlings could get a similar experience visiting parts of New Jersey in January.

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